NAME
Taint::Runtime - Runtime enable taint checking
SYNOPSIS
### sample "enable" usage
#!/usr/bin/perl -w
use Taint::Runtime qw(enable taint_env);
taint_env();
# having the keyword enable in the import list starts taint
### sample $TAINT usage
#!/usr/bin/perl -w
use Taint::Runtime qw($TAINT taint_env);
$TAINT = 1;
taint_env();
# taint is now enabled
if (1) {
local $TAINT = 0;
# do something we trust
}
# back to an untrustwory area
### sample functional usage
#!/usr/bin/perl -w
use strict;
use Taint::Runtime qw(taint_start is_tainted taint_env
taint untaint
taint_enabled);
### other operations here
taint_start(); # taint should become active
taint_env(); # %ENV was previously untainted
print taint_enabled() ? "enabled\n" : "not enabled\n";
my $var = taint("some string");
print is_tainted($var) ? "tainted\n" : "not tainted\n";
$var = untaint($var);
# OR
untaint \$var;
print is_tainted($var) ? "tainted\n" : "not tainted\n";
DESCRIPTION
First - you probably shouldn't use this module to control taint. You
should probably use the -T switch on the commandline instead. There are
a somewhat limited number of legitimate use cases where you should use
this module instead of the -T switch. Unless you have a specific and
good reason for not using the -T option, you should use the -T option.
Taint is a good thing. However, few people (that I work with or talk to
or discuss items with) use taint even though they should. The goal of
this module isn't to use taint less, but to actually encourage its use
more. This module aims to make using taint as painless as possible (This
can be an argument against it - often implementation of security implies
pain - so taking away pain might lessen security - sort of).
In general - the more secure your script needs to be - the earlier on in
your program that tainting should be enabled. For most setuid scripts,
you should enable taint by using the -T switch. Without doing so you
allow for a non-root user to override @INC which allows for them to put
their own module in the place of trusted modules. This is bad. This is
very bad. Use the -T switch.
There are some common places where this module may be useful, and where
most people don't use it. One such place is in a web server. The -T
switch removes PERL5LIB and PERLLIB and '.' from @INC (or remove them
before they can be added). This makes sense under setuid. The use of the
-T switch in a CGI environment may cause a bit of a headache. For new
development, CGI scripts it may be possible to use the -T switch and for
mod_perl environments there is the PerlTaint variable. Both of these
methods will enable taint and from that point on development should be
done with taint.
However, many (possibly most) perl web server implentations add their
own paths to the PERL5LIB. All CGI's and mod_perl scripts can then have
access. Using the -T switch throws a wrench into the works as suddenly
PERL5LIB disappears (mod_perl can easily have the extra directories
added again using push @INC, '/our/lib/dir';). The company
I work for has 200 plus user visible scripts mixed with some mod_perl.
Currently none of the scripts use taint. We would like for them all to,
but it is not feasible to make the change all at once. Taint::Runtime
allows for moving legacy scripts over one at a time.
Again, if you are using setuid - don't use this script.
If you are not using setuid and have reasons not to use the -T and are
using this module, make sure that taint is enabled before processing any
user data. Also remember that BECAUSE THE -T SWITCH WAS NOT USED %ENV IS
INITIALLY NOT MARKED AS TAINTED. Call taint_env() to mark it as tainted
(especially important in CGI scripts which all read from
$ENV{'QUERY_STRING'}).
If you are not using the -T switch, you most likely should use the
following at the very top of your script:
#!/usr/bin/perl -w
use strict;
use Taint::Runtime qw(enable taint_env);
taint_env();
Though this module allows for you to turn taint off - you probably
shouldn't. This module is more for you to turn taint on - and once it is
on it probably ought to stay on.
NON-EXPORTABLE XS FUNCTIONS
The following very basic functions provide the base functionality.
_taint_start()
Sets PL_tainting
_taint_stop()
Sets PL_tainting
_taint_enabled()
View of PL_tainting
_tainted()
Returns a zero length tainted string.
$TAINT VARIABLE
The variable $TAINT is tied to the current state of taint. If $TAINT is
set to 0 taint mode is off. When it is set to 1 taint mode is enabled.
if (1) {
local $TAINT = 1;
# taint is enabled
}
EXPORT FUNCTIONS
enable/disable
Not really functions. If these keywords are in the import list,
taint will be either enabled or disabled.
taint_start
Start taint mode. $TAINT will equal 1.
taint_stop
Stop taint mode. $TAINT will equal 0.
taint_env
Convenience function that taints the keys and values of %ENV. If the
-T switch was not used - you most likely should call this as soon as
taint mode is enabled.
taint
Taints the passed in variable. Only works on writeable scalar
values. If a scalar ref is passed in - it is modified. If a scalar
is passed in (non ref) it is copied, modified and returned. If a
value was undefined, it becomes a zero length defined and tainted
string.
taint(\$var_to_be_tainted);
my $tainted_copy = taint($some_var);
For a stronger taint, see the Taint module by Dan Sulgalski which is
capable of tainting most types of data.
untaint
Untaints the passed in variable. Only works on writeable scalar
values. If a scalar ref is passed in - it is modified. If a scalar
is passed in (non ref) it is copied, modified and returned. If a
value was undefined it becomes an untainted undefined value.
Note: Just because the variable is untainted, doesn't mean that it
is safe. You really should use CGI::Ex::Validate, or
Data::FormValidator or any of the Untaint:: modules. If you are
doing your own validation, and once you have put the user data
through very strict checks, then you can use untaint.
if ($var_to_be_untainted =~ /^[\w\.\-]{0,100}$/) {
untaint(\$var_to_be_untainted);
}
my $untainted_copy = untaint($some_var);
taint_enabled
Boolean - Is taint on.
tainted
Returns a zero length tainted string.
is_tainted
Boolean - True if the passed value is tainted.
taint_deeply
Convenience function that attempts to deply recurse a structure and
mark it as tainted. Takes a hashref, arrayref, scalar ref, or scalar
and recursively untaints the structure.
For a stronger taint, see the Taint module by Dan Sulgalski which is
capable of tainting most types of data.
TURNING TAINT ON
(Be sure to call taint_env() after turning taint on the first time)
#!/usr/bin/perl -T
use Taint::Runtime qw(enable);
# this does not create a function called enable - just starts taint
use Taint::Runtime qw($TAINT);
$TAINT = 1;
use Taint::Runtime qw(taint_start);
taint_start;
TURNING TAINT OFF
use Taint::Runtime qw(disable);
# this does not create a function called disable - just stops taint
use Taint::Runtime qw($TAINT);
$TAINT = 0;
use Taint::Runtime qw(taint_stop);
taint_stop;
CREDITS
C code was provided by "hv" on perlmonks. This module wouldn't really be
possible without insight into the internals that "hv" provided. His post
with the code was shown in this node on perlmonks:
http://perlmonks.org/?node_id=434086
The basic premise in that node was the following code:
use Inline C => 'void _start_taint() { PL_tainting = 1; }';
use Inline C => 'SV* _tainted() { PL_tainted = 1; return newSVpvn("", 0); }';
In this module, these two lines have instead been turned into XS for
runtime speed (and so you won't need Inline and Parse::RecDescent).
Note: even though "hv" provided the base code example, that doesn't mean
that he necessarily endorses the idea. If there are disagreements,
quirks, annoyances or any other negative side effects with this module -
blame me - not "hv."
AUTHOR
Paul Seamons (2005)
C stub functions by "hv" on perlmonks.org
LICENSE
This module may be used and distributed under the same terms as Perl
itself.